The invention pertains to a process for sealing a multilayer article against environmental degradation and more particularly, to a process for sealing a multilayer article such as a multilayer photovoltaic cell comprising a photoactive layer disposed on a length of flexible substrate.
Photovoltaic cells are made by depositing various layers of materials on a suitable substrate which can be rigid (e.g., glass or a silicon wafer) or flexible (e.g., a thin metal or polymer sheet). U.S. Patent Publication No. US 2009/0223551 A1, for example, describes a process for fabricating a solar cell, i.e., a photovoltaic device, in a continuous roll to roll process wherein the substrate comprises a length of flexible foil. A set of multiple layers comprising the photovoltaic device are formed on a section of the substrate, i.e., a bare flexible substrate is supplied, and a complete solar cell device is realized in a continuous process. Once completed, the flexible solar cell can be re-rolled onto a take-up spool.
In the manufacture of flexible thin film Cu(In,Ga)Se2 (CIGS) solar cells, for example, one of the most important aspects is effectively sealing the completed multi-layer device against moisture degradation. There remains a need for a method to produce a barrier layer, i.e., a flexible protective top sheet, on a flexible multi-layer device that has the flexibility of the device, surface properties to resist or prevent moisture penetration, and can be used in a roll-to-roll process of the type used for fabricating CIGS and the like photovoltaic cells.